Match filters for a real time fingerprint sensor and verification system

ABSTRACT

A real time fingerprint verification system includes a recording device and a verification device each having a fingerprint scanner for generating a flat, dimensionally undistorted, high contrast, fingerprint image, and an intensity sensitive, spatial light modulator (SLM) for receiving and transforming the flat fingerprint image into a planar, coherent light image. In the recording device, the planar coherent light image beam of the fingerprint from the SLM is Fourier transformed, and input into a microscope objective lens system which expands the Fourier transformed beam image sufficiently to allow mechanical blocking of its central portion or order, whereupon it is directed to interact as an object beam with a reference beam from the particular coherent light source to record a holographic matched filter. In the verification device, the planar coherent light image beam of the fingerprint is Fourier transformed and input into a microscope objective lens system to allow similar mechanical blocking of its central portion or order whereupon it is directed to interrogates a previously recorded holographic matched filter of a fingerprint image as an object beam for determining a match or not between the respective recorded and interrogating images. The spatial light modulator (SLM) in both the respective recording and verification devices enables phase correlation (optical path length determination) of one device to another device. X-Y alignment and rotational orinentation of the respective real time image and holographic matched filter image is accomplished by jittering (orbiting and angularly oscillating) either the interrogating object beam, real time, relative to the matched filter or visa versa.

RELATED APPLICATIONS

This application is division of application Ser. No. 08/853,850 filedMay 9, 1997 in the United States of America by Thomas M. Corboline andentitled Ramendra D. Bahuguna "REAL TIME FINGERPRINT SENSOR ANDVERIFICATION SYSTEM" now U.S. Pat. No. 6,002,499 issued Dec. 18, 1999which in turn, comprised a continuation-in-part of: (i) application Ser.No. 08/499,673 filed Jul. 7, 1995 in the United States of America byRamendra D. Bahuguna and Thomas M. Corboline entitled "A PRISMFINGERPRINT SENSOR USING A HOLOGRAPHIC OPTICAL ELEMENT" now U.S. Pat.No. 5,629,764 issued May 13, 1997 and (ii) application Ser. No.08/694,671 filed Aug. 9, 1996 in the United States of America byRamendra D. Bahuguna entitled "A MINIATURE FINGERPRINT SENSOR USING ATRAPEZOIDAL PRISM AND A HOLOGRAPHIC OPTICAL ELEMENT now U.S. Pat. No.5,892,599 issued Apr. 6, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a system for capturing high contrast, detailedoptical fingerprint images, and recording the fingerprint images as anobject in a Fourier transform hologram and subsequently comparing aFourier transform of high contrast, detailed optical fingerprint imagespresented in a coherent object beam with that recorded in a Fouriertransform hologram fingerprint matched filter for verification purposes.

2. Description of the Prior Art

Typically fingerprint capture and verification systems includemechanisms for optically capturing images of a fingerprint, mechanismsfor optically comparing or interrogating records of fingerprint imageswith contemporaneous fingerprint images, and signalcomparison/computational processors (computers) for analyzing andproviding output indicative or as a consequence of a match between apermanent fingerprint record and a contemporaneously capturedfingerprint image. The preferred fingerprint record for such systems isa hologram or holographic interference pattern created utilizing anobject beam and a reference beam emanating from a common coherent(laser) light/radiation source. The object beam has or containsinformation, i.e., a fingerprint image (or its Fourier transform). Thereference beam contains no information or image. The respective beamsinterfere within a volume of a holographic recording medium generatingan interference pattern. Holograms have the unique property ofreconstructing the corresponding reference or object light beams whensubsequently illuminated by a light beam corresponding with therecording object or reference beam respectively. [See generally VanNostrand's Scientific Encyclopedia 8^(th) Ed. "Hologram" pp. 1602-1604.]

When interrogating a hologram for pattern identification, comparisonand/or verification purposes, a hologram of the Fourier transform of theimage, variously described as a spatial or matched filter, is preferred.In an optical context, a Fourier transform of an image is basicallyperformed by a lens transforming an image from spatial to phase domainat a plane containing the focal point of the particular lens. U.S. Pat.No. 3,716,301 Caulfield et al, [col. 4, 11. 12-64] presents anexplanation generally describing both the nature of and how to record ahologram of a Fourier transform of a fingerprint image. [It should berecognized that the particular fingerprint image described by Caulfielet al is dimensionally compressed vertically by a factor of 1/√2.]

In the Applicant's co-pending applications Ser. No. 08/499,673 filedJul. 7, 1995 and Ser. No. 08/694,671 filed Aug. 8, 1996 an opticaldevice utilizing the phenomenon of total internal reflection and aholographic phase grating for capturing and provided a dimensionallyundistorted optical image of a fingerprint is suitable both for: (i)creating a permanent record of the captured image and (ii) interrogatinga previously recorded permanent finger print record.

It should be appreciated that while optically undistorted fingerprintimages photographically recorded in transparencies or printed onphotographic paper are suitable for manual or visual comparisonpurposes, because of thickness variations in the recording media, suchtransparency and print images typically should not be used directly forgenerating holograms of Fourier transforms of such images, i.e., thespatial or matched filters of the recorded fingerprint images.

Also, existing real time fingerprint verification systems whichinterrogate holographic Fourier transforms or spatial/matched filters offingerprint images prerecorded onto an identification card areparticularly prone to false positive verifications especially when thematched filters are flooded with light scattered into the interrogatingoptical beam by "wiping" smears or streaks on the fingerprint capturesurface. In such instances, the Fourier transform of the scattered lightin the interrogating beam partially correlates with the pattern recordedin the matched filter thus generating optical output at a detectorindicating partial correlation. In particular, while it is recognizedthat the fingerprints of an individual are uniquely different from thoseof others, the degrees of general similarity between fingerprints ofdifferent individuals are typically greater than the degrees ofdifference. For example, spacing between print ridges and pores per unitlength along a print ridge in the same region of right index fingerhuman fingerprints can in fact essentially coincide except for one ortwo distinctive differences. It is also recognized that humanfingerprints typically fall into distinctive patterns or groups, whichfingerprint experts currently use for cataloguing purposes. The upshotis that an interrogating coherent object beam containing any fingerprintimage when Fourier transformed, will generate a correlation light signalfrom any Fourier transform fingerprint matched filter. The intensity ormagnitude of the correlation light signal is indicative of the degree ofcorrelation between the real time Fourier transform interrogating objectbeam and the recording object beam used to create the particularfingerprint matched filter. [See U.S. Pat. No. 5,600,485, Iwaki et al,and U.S. Pat. Nos. 4,750,153; 4,837,843; 4,860,254 & 4,961,615, Wenchkoet al which describe associative memory systems which utilize thedescribed properties of holographic Fourier transforms matched filtersin combination with Spatial Light Modulators (SLMs) for patternrecognition.] Thus scattered light flooding an input interrogatingobject beam of existing real time fingerprint verification systems canadd sufficiently to the correlation optical light signal to change anactual negative correlation to a positive verification.

Existing real time fingerprint verification systems also presentalignment and orientation problems. In other words, it is nearlyimpossible for a finger to be placed in exactly the same position twiceon an input scanner surface. This means that it is nearly impossible tocreate an identical planar image of a fingerprint image (or its Fouriertransform) that corresponds in position to that pre-recorded in amatched filter, a problem that becomes even more difficult whendifferent scanner and processing optics are used respectively to captureand record the matched filter image and to capture and interrogate therecorded matched filter with an image.

Alignment typically refers to X-Y position correlation between theFourier transformed image in the interrogating beam and thatpre-recorded in the matched filter, i.e., assuming the Fouriertransformed image in the interrogating object beam is in the same planeas the Fourier transformed image pre-recorded in the matched filter, itis the displacement of the interrogating image in the X-Y plane of thematched filter relative to the matched filter image. U.S. Pat. No.5,541,994, Tomko et al [Col. 8 line 52-.Col. 9, 1. 38] addresses theproblem of X-Y correspondence by scanning for location of output peaksof a Fourier transformed fingerprint image transmitted through a spatiallight modulator (SLM) receiving input from stored reference filters todefine an array of values.

Orientation typically refers to the angular or rotational positioncorrelation of the interrogating image with the matched filter imageassuming the respective images are at the same X-Y position, i.e., thedegree to which the Fourier transformed interrogating object image isrotated relative to the Fourier transformed matched filter image. U.S.Pat. No. 3,716,301 Caulfield et al [Col. 7, 11. 28-66] suggests a both adynamic and static optical solution to the problem of orientation. Thedynamic solution suggestion involves rotating a dove prism to achieve"opto-mechanical rotational alignment" of the interrogating object imagewith that recorded in the matched filter [col. 5, 11. 55-62], The staticsolution suggestion involves spatially multiplexed Fourier transformfingerprint images recorded angularly around a common axis in thematched filter, the angle of incidence of the creating reference beambeing slightly different at each different-rotational position. Anaffirmation-negation signal discrimination circuit receives input fromdetectors located at different positions to provide a threshold signalindicative of a matched. In contrast, U.S. Pat. No. 5,095,194 Barbanell[Col. 5, 11. 16-32] teaches a simpler dynamic solution contemplatingmovement of the finger on the input surface as the mechanism forachieving correlation of position of the interrogating Fouriertransformed real time image with that recorded in the matched filter toproduce a threshold optical signal at an appropriately located detectorto detect a reconstructed reference beam pulse in the event of acorrelation as the position of interrogating image sweeps aroundresponsive to finger movements on the input surface.

Another factor affecting performance of coherent light--holographicmatched filter optical systems for authenticating or verifying anidentity is phase correlation. As previously mentioned, a coherent lightfingerprint image taken from a transparency should not be used to createa holographic matched filter because of thickness variations in thetransparency. Such thickness variations mean differences in optical pathlength, i.e., variations in phase in the plane of such Fouriertransformed image recorded in a matched filter. Accordingly, when thematched filter is subsequently interrogated, real time, by a Fouriertransformed of a captured fingerprint image, the magnitude ofcorrelation will depend on the degree of correspondence (or lackthereof) of phase-of the interrogating object beams with thatpre-recorded in the plane of the image recorded in the matched filter.Phase correlation problems also arises out of differences in opticalpath lengths between the recording optical systems creating matchedfilters and the optical systems comparing real time, captured images tothose recorded in the matched filter. For example, even assumingalignment and rotational correlation of the respective interrogating andmatched filter images in a credit card system of the type contemplatedin U.S. Pat. No. 5,095,194 Barbanell, infinitesimal differences inposition on the optical axis of the card matched filter in theverification apparatus can mean the difference between a thresholdcorrelation signal or not.

SUMMARY OF THE INVENTION

The invented real time fingerprint verification system includes arecording apparatus and a verification apparatus each having afingerprint scanner for generating a flat, dimensionally undistorted,high contrast, fingerprint image, and an intensity sensitive, spatiallight modulator (SLM) for receiving and transforming the flatfingerprint image into a planar, coherent light image of thefingerprint. The SLM eliminates phase variations in the respectiveplanar, coherent light output images, and permits optical path length ofa recording apparatus to adjusted relative to that of a verificationapparatus to assure phase correlation between the pre-recorded matchedfilter produced by the recording apparatus and the interrogatingcoherent object beam of a particular verification apparatusinterrogating that particular created pre-recorded matched filter.

The planar coherent light image beam of the fingerprint emanating fromthe SLM in the recording apparatus is Fourier transformed, and inputinto a microscope objective lens system for expanding the focus to allowmechanical blocking of its central order per the teachings of U.S. Pat.No. 3,716,301 Caulfield et al. The so modified beam is then directed tointeract as an object beam with a reference beam from the particularcoherent light source to record a holographic matched filter. Similarly,in the verification apparatus, a planar coherent light image beam of thefingerprint taken from the SLM is Fourier transformed and expanded toallow mechanical blocking of its central order whereupon it is directedto interrogate (as an object beam), a previously recorded holographicFourier transform matched filter of a fingerprint image for determininga match or not between the respective matched filter and interrogatingimages.

The invented real time fingerprint verification system contemplates averification device having an optical/mechanical system for eitherjittering (dimensionally orbiting and rotating) the just capturedundistorted fingerprint image written into a spatial light modulator(SLM), or jittering the pre-recorded matched filter relative to theoptical axis of the system for assuring coincidence between a real timecaptured and transformed image and that pre-recorded in a matchedfilter.

In an embodiment of the invented system, alignment or X-Y correlation ofthe planar, magnified and blocked, Fourier transformed fingerprintimages within the interrogating object beam with that recorded in theholographic matched filter in the plane of the matched filter isaccomplished by suitably scanning or orbiting the interrogation objectbeam, real time, relative to the holographic matched filter or visaversa. In particular, the input coherent light beam to read the SLM isin one embodiment simultaneously deflected along x and y axes of a planeperpendicular to the beam axis using a pair of reflecting surfacesdriven by an electromagnetic vibrator per conventional bar code scanningtechniques. [See U.S. Pat. No. 5,581,067, Grosfeld, et al and U.S. Pat.No. 5,486,944, Bard, et. al.] The simultaneous deflections of thecoherent light input beam orbits or scans the particular transformed,magnified and blocked output object beam relative to the optical axis ofthe system.

Orientation or rotational correlation of the respective recorded andinterrogating planar Fourier transformed fingerprint images isaccomplished preferably by inducing a slight periodic angularoscillation rotating the light beam input into or output from thespatial light modulator (SLM) about its the optical axis, oralternatively by inducing a similar slight periodic angular oscillationfor rotating the matched filter assembly angularly about its opticalaxis, i.e., an axis perpendicular to the plane of the recorded filterimage. An exemplary embodiment of the invented system contemplates adove prism rotationally suspended or mounted in a manner which permits aslight rotation about the optical axis. The prism is torsionallyrestrained to a quiescent or rest position. Perturbing the dove prismassembly (electromagnetically, acoustically or otherwise) induces slightperiodic angular rotational oscillation in the writing light beam inputinto or read from the SLM. In either instance, the coherent light outputimage beam taken from the SLM, subsequently transformed, expanded,blocked and input into a matched filter periodically oscillates rotatingthrough a angle about its optical axis twice the magnitude of the prismoscillation angle.

In another embodiment of the invented real time verification system, asnapshot of a flat fingerprint image is captured, digitized andprocessed computationally for dimensionally rotating and orbiting(jittering) an image written to an electronically addressed, digitallycontrolled SLM which when read, outputs a fingerprint image orbiting androtating (jittering) in a plane for interrogating a matched filter. [SeeU.S. Pat. Nos. 5,022,750 & 5,108,172, Flask which describes activematrix reflective projection systems and U.S. Pat. No. 5,600,485 Iwakiet al which describes an optical pattern recognition system utilizing apair of SLMs.]

Still another embodiment of the invented real time fingerprintverification system contemplates a verification device having anoptical/mechanical system for either jittering (dimensionally rotatingand orbiting) the just captured undistorted fingerprint image writteninto a spatial light modulator (SLM), or jittering the pre-recordedmatched filter relative to the optical axis of the system.

The unique features and advantages afforded by, as well as the novelaspects of the invented real time fingerprint verification system aremore fully explained with reference to the following detailedexplanation in context of drawings depicting schematics of demonstrativeand exemplary optical systems for simply and reliably identification byauthenticating or matching fingerprints presented real time by differentindividuals to those pre-recorded in hologram matched filters.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic of an exemplary optical table setup illustratingthe essential components of the invented real time fingerprintverification system utilizing a dove prism for angularly oscillating andvibrating mirrors for orbiting the fingerprint image.

FIG. 2 is a schematic of an exemplary optical table setup illustratingthe essential components of the invented real time fingerprintverification system utilizing a computer addressed, digitally controlledspatial light modulator (SLM) for both angularly oscillating andorbiting the fingerprint image.

FIG. 3 is an optical schematic of an exemplary `breadboard` of aminiaturized embodiment of an optically addressed verification devicefor the invented system.

FIG. 4 is an optical schematic of an exemplary `breadboard` of aminiaturized embodiment of an exemplary verification device of theinvented system utilizing an electronically addressed verificationdevice for the invented system.

DETAILED DESCRIPTION OF PREFERRED AND EXEMPLARY EMBODIMENTS

FIGS. 1 and 2 schematically show an exemplary optical table setupdemonstrating both the recording and the verifying apparatus of theinvented real time fingerprint verification system. In particular, anundistorted fingerprint image 11 is obtained from a finger 12 utilizinga finger print scanner 13 of the type described in co-pendingapplications Ser. No. 08/499,673 filed Jul. 7, 1995 in the United Statesof America by RAMENDRA D. BAHUGUNA and THOMAS M. CORBOLINE entitled "APRISM FINGERPRINT SENSOR USING A HOLOGRAPHIC OPTICAL ELEMENT"; and (ii)Ser. No. 08/694,671 filed Aug. 8, 1996 in the United States of Americaby RAMENDRA D. BAHUGUNA entitled "A MINIATURE FINGERPRINT SENSOR USING ATRAPEZOIDAL PRISM AND A HOLOGRAPHIC OPTICAL ELEMENT.

In the optically addressed system, (FIG. 1) the undistorted fingerprintimage 11 is optically focused by a lens L₁ onto the write face 14 of anintensity sensitive Spatial Light Modulator SLM. In the computeraddressed system (FIG. 2) an undistorted graphical video image of thefingerprint 11 is produced by the scanner 13 and input into a computersystem 15. The computer system digitizes the graphical video fingerprintimage and electronically drives and inputs the digitized graphical videofingerprint image onto an electronically addressed, write face 14' of adigitally controlled Spatial Light Modulator SLM. With the computeraddressed system the source of the image of the fingerprint could alsobe a computer accessed database or other digital signal storage sourcefrom which digitized graphics of previously captured undistortedfingerprint images are recorded and stored for retrieval. In both theoptically and computer addressed systems, the read faces 16 of therespective SLMs are conventionally read using a coherent light or objectbeam 17 originating from a laser for transforming the undistortedfingerprint image 11 image written onto the respective write faces 14 &14' of the SLMs into a coherent fingerprint image beam 18. In theexamples illustrated, a polarizing beam splitter 19 directs the objectbeam 17 from the laser onto the read face 16 of the SLM and thenoptically transmits the coherent fingerprint image beam 18 reflectedfrom the read face 16 of the SLM.

The recording apparatus also requires a reference beam 21 to create ahologram matched filter, and, in the exemplary optical table setups, abeam splitter BS, splits a reference beam 21 from a source beam 22 gatedfrom a laser by an electronic shutter 25. Steering mirrors M₁, M₂, & M₃direct or steer the respective object and reference beams 17 & 21 splitfrom the source laser beam 22 to their respective optical destinations,i.e. the object beam 17 to the polarizing beam splitter 19, and thereference beam 21 to the hologram image plane H of the optical setup.Per conventional techniques, both the object and reference beams 17 & 21should be expanded and cleaned (schematically indicated at 23) using,for example, a 20× microscope objective and a 10-25 m pinhole. Theexpanded and cleaned object and reference beams 17 & 21 are then shaped(collimated) by lens L₃ & L₄, respectively. Spacing between steeringmirrors M₁ & M₃ is adjustable for matching (correlating) the opticalpath length of the reference beam 21 from the beam splitter BS to thehologram image plane H to the optical path length of the object beam 17from the beam splitter BS via the read face 16 of the SLM to thehologram plane H.

The verification apparatus requires a detector located for detecting andgenerating a signal in the event of a threshold match between a hologrammatched filter 24 and a Fourier transformed interrogating/object beam26. As schematically shown in the exemplary optical table setups, thereconstructed light beam 27 scattered/diffracted-from the hologrammatched filter 24 is directed by steering mirror M₆ via a focusing lensL₅ onto an appropriately located linear photo detector CCD, in theembodiments illustrated, a Charge Couple Device.

Looking at FIG. 1 (the optically addressed system), mirrors M₄ and M₅are oscillated per conventional bar code scanning techniques foroptically deflecting the object beam 17 directed via collimating lens L₃through beam splitter 19 onto the read face 16 of the SLM which inducesa suitable scanning orbit to the coherent fingerprint image beam 18reflecting from the read face 16 of the SLM. [Please refer to U.S. Pat.No. 5,581,067, Grosfeld, et al and U.S. Pat. No. 5,486,944, Bard, er.al. and prior art references cited in the patents for teachings relativeto orbiting/scanning a light beam in appropriate patterns.]

In particular, bi-directional oscillatory motion in the coherentfingerprint image beam 18 can be achieved by appropriately mounting orsuspending one or more optically reflecting elements in an assembly offlex elements and perturbing the assembly with interacting magneticfields or otherwise. While such perturbed optically reflecting elementscan possibly be located anywhere in the optical path after the objectbeam 17 is expanded and cleaned and the hologram matched filter 24, itis recommended that they be located in the optical path before the SLM.The objective is to cause the pattern (Fourier transformed fingerprintimage) in the interrogating/object beam 26 to move or oscillate in thehologram plane H without significantly changing optical path length,i.e. phase distribution in the plane of the focus. In particular, theoptical path length (distance) between the read face 16 of the SLM and amounted or loaded hologram matched filter 24 in the verificationapparatus is a known. Accordingly, it is possible to pre-record thehologram matched filter 24 with a (different) recording apparatus suchthat the optical path length between the read face 16 of the recordingSLM and the hologram plane H, i.e. the phase distribution presented bythe Fourier transformed recording beam 26, will correlate sufficientlywith that of the particular verification apparatus such that, in theevent of a match, the particular matched filter 24 when mounted orloaded for interrogation, will scatter/diffract a strong (largemagnitude) optical signal (reconstructed reference beam 27) to the CCD.In essence, while the position of the captured `real time` fingerprintimage 11 written to the write face 14 of the verifying SLM might not beat the same position as that written to the write face 14 of therecording SLM for recording its Fourier transform as a matched filter23, nevertheless, the originating planes of the respective interrogatingand recording fingerprint image beams 18 can be optically correlated.Locating perturbed optically reflecting elements before the SLM in theverification apparatus transforms or orbits the X-Y position of thefingerprint pattern read from the read face of SLM such that its Fouriertransformed phase distribution in the hologram plane H at some pointwill sweep through coincidence with the Fourier transform fingerprintphase image recorded in the matched filter. And, in the event of a matcha strong optical signal will be scattered/diffracted to the photodetector CCD.

Indicated in FIG. 1, as suggested by Caulfield et al, a dove prism 31 isutilized to rotationally oscillate the orientation or rotationalposition of the fingerprint image 11 about its optical beam axis. Inparticular, the dove prism 31 is suspended or mounted in a manner whichpermits a slight rotation about its optical axis. Ideally, the prismshould be torsionally restrained to a quiescent or rest position suchthat perturbing the assembly (electromagnetically, acoustically orotherwise) causes the prism 31 to oscillate like a pendulum through aslight angle. Assuming the pendulum axis and optical axis coincide, theundistorted fingerprint image 11 input to write face 14 of the SLM willrotationally oscillate through an angle twice that of the prism. Thus,the rotational orientation of the coherent fingerprint image beam 18read from the SLM, subsequently Fourier transformed into theobject/interrogating beam 26 input to the matched filter 24 will alsoperiodically oscillate rotating through a angle about its optical axistwice that of the prism oscillation angle.

As with the deflecting mirrors M₄ & M₅, a skilled optical technologistshould recognize that optically, the dove prism 31 may be locatedanywhere in the optical path of the exemplary set up from thefingerprint scanner 13 to the hologram plane H. Such skilledtechnologist should also recognize that there are other well knownoptical elements which rotate a planar image about an optical beam axis,e.g., a conventional roof prism. In any case, it is recommended that thedove prism 31 or other optical rotator element be located in the opticalpath between the fingerprint scanner 13 and the read face 14 of the SLMto avoid complications associated with correlating optical path lengthswhen recording matched filters for a particular type verificationapparatus. This is because a dove prism 31 or other optical rotatorelement, if interposed between the read face 16 of the SLM and thehologram plane H, will change (lengthen) the optical path and thereforephase distribution of the Fourier transformed beam in the hologram planeH. Such change in optical path would necessarily have to be correlatedto the optical path of the recording apparatus used in creation of theFourier transform matched filter 24. In an optical table set up, whereboth the optical elements and positions of the recording apparatus andthe verification apparatus between the read face 16 of the SLM and thehologram plane H are the identical, such correlations are feasible, butthey are not for different field apparatus because no two opticalcomponents such as dove prisms demonstrate identical or matching opticalproperties.

Optimally, both the X-Y scanning mechanism and the orientationoscillating mechanism of verification apparatus could be combined into acommon `jitter` optical/mechanical mechanism. For example, byappropriately choosing optical parameters (size, index of refraction andincidence angles) of the optical rotator (prism) element, located tooperate on the the coherent fingerprint image beam 18 it is possible tolaterally displace the output beam relative to the input beam.Accordingly, slight angular oscillation or jitter of such opticalrotator element about the input optical axis, would not onlyrotationally oscillate the output image beam about its optical axis, butalso would orbit it in the X-Y plane. And, by choosing appropriatesuspension and perturbing mechanisms in the assembly mounting suchoptical jitter element, it should be possible to cause the output beamfrom the rotator element not only to rotationally oscillate but also toscan or orbit in a pattern, which in the X-Y, plane, precesses about aquiescent point ideally coinciding with its optical output axis, similarto the manner a point on a plucked vibrating string elliptically orbitsand precesses about the quiescent string position. In an ideal world,where gross alignment of the matched filter in the hologram plane withthe optical axis of the interrogating object beam 26 can be assumed,such a jitter mechanism would be incorporated into the optics of thescanner 13 or operate on the captured undistorted fingerprint image beamdelivered by the scanner 13 before it is input into the SLM. Anotherpossible alternative would be to provide a mechanism for jittering theassembly mounting or loading the matched filter in a plane perpendicularto the optical axis of a verification apparatus

Ultimately, however, from a point of view of simplicity, and economy ofconstruction, per the teachings of Barbanell, (supra), the betterpractice might be to allow the person whose fingerprint is beingcaptured real time for verification purposes to rotationally oscillateand orbit the captured undistorted fingerprint image 11 by moving achosen finger on the input surface of the scanner. In fact, such asimple solution could add substantially to the degree security affordedby the invented system in that, when one or more fingerprint images arecaptured for recording a matched filter 24, the presenting person knowswhich of the ten finger(s) used, and the approximate rotationalorientation of the chosen finger(s) 12 on the input surface of thescanner 13.

In fact, as illustrated in FIG. 2, in the computer addressed system, forverification, the computer system driving the write face 14' of the SLMcan be appropriately programmed for both rotationally oscillating andorbiting (jittering) the captured undistorted fingerprint image 11delivered by the scanner 13 it, about the write face 14' of the SLM.However, a skilled optical technologist should realize that the focus inthe focal plane, i.e. the center of the Fourier transform interrogatingimage, will remain on the optical axis of interrogating beam 26regardless of the X-Y position of the fingerprint image on the writeface 14' of the SLM. Accordingly, in those instances where grossalignment in the hologram plane H can not be assured between thepre-recorded matched filter mounted/loaded in the verification apparatusand the optical axis of the Fourier transformed interrogating beam 26,deflecting mirrors M₄ and M₅, as previously described with reference tothe optically addressed system shown in FIG. 1, may be located foroptically scanning or orbiting the interrogation object beam 26 realtime, relative to the holographic matched filter 24

In both the optically addressed and the computer addressed embodimentsof the invented real time fingerprint capture and verification systems,(FIGS. 1 & 2) the coherent fingerprint image beam 18 transmitted by thebeam polarizing beam splitter 19 is Fourier transformed by lens L₂ anddirected through a λ/2 waveplate to rotate beam polarization 90°. TheFourier transform of the object/interrogating image beam 26 (the focus)formed by L₂ is expanded by a microscopic objective lens MO. The centralorder of the Fourier transform of the image is mechanically blockedusing conventional techniques and focused on the hologram plane H.

In the recording apparatus, a thermoplastic holographic film recordingmedium is located in the hologram plane H whereupon the expanded andblocked object/interrogating beam 26 interferes with the reference beam21 for recording a hologram of the expanded and blocked Fouriertransform of the fingerprint image 11. When recording the matchedfilter, as well as when interrogating the such matched filter, theskilled optical technologist should appreciate that the preferredpolarization of the respective interfering reference and Fouriertransformed object/interrogating beams 21 & 26 should be perpendicularto the plane of the angle between the respective interfering beams inorder to maximize the diffraction efficiency of the generated andinterrogated hologram. For example, in the perspective of the exemplaryoptical table set-ups presented in FIGS. 1 & 2, the reference andobject/interrogating beams 21 & 26 should be vertically polarized.

FIGS. 3 & 4 schematically show a top view of exemplary breadboardset-ups of a miniaturized, optically addressed and computer addressedverification device, In particular, the respective verification deviceseach include an SLM with a write face 41 and a read face 42 forintroducing an image (a fingerprint pattern) into the optical system. Anexpanding coherent light beam 43 originating from a laser diode isdirected by a pair of turning mirrors through a first achromatic doubletlens for collimating then is reflected by a polarizing beam splitteronto the read face 42 of the SLM. A coherent fingerprint image beam 44reflects from the read face 42 of the SLM and is transmitted by thepolarizing beam splitter then Fourier transformed (directed to a focus)by a second achromatic doublet lens. A microscope objective expands thefocus of the second achromatic doublet lens into an interrogating imagebeam 46 which is directed for interrogating a matched filter by a mirror47. The central order of the transformed image in the interrogatingimage beam 46, if necessary, can be conventionally blocked mechanicallyin the optics of the microscope objective or alternatively on thesurface of the mirror 47. To explain, if the central order of theFourier transforms of the fingerprint images recorded as matched filtershave been eliminated, then light in the central order of aninterrogating Fourier transform of a just captured fingerprint imagewould not be scattered/diffracted for reconstruction of the constructingreference beam 48. However, such central order interrogating light mightwell add unacceptably to a partial signal when different, slightlymisaligned and/or misoriented interrogating Fourier transform imagebeams are scattered/diffracted by the matched filter. The reconstructedreference beam 48 scattered/diffracted from the matched filter isfocused by a collector lens 49 onto a photo diode array or ccd detectorwhich provides an appropriately large signal at a particular position inthe event of a match between the transformed image in the interrogatingbeam and that pre-recorded in the matched filter.

Referring to FIG. 3, in the optically addressed system, a laser diodeilluminates a fingerprint input surface 52 of a fingerprint sensor 53via mirror 51. The fingerprint sensor is preferably of the typedescribed in Applicant Bahuguna's co-pending application Ser. No.08/694,671 filed Aug. 8, 1996 for capturing and projecting anundistorted fingerprint image. The fingerprint image is received by aconventional camera objective imaging optical system 56 and projectedonto the write face 41 of the SLM. A jitter optical/mechanical mechanismmaybe incorporated into the camera's optical system 56 for rotating andorbiting the captured fingerprint image on the write face 41 of the SLM.The focal region of the coherent fingerprint image beam 44 reflectedfrom the read face 42 of the SLM may also be jittered in the X-Y planeof the match filter by an appropriate mechanism periodically tilting oneor more of the steering mirrors directing the coherent light beams 43 &44 to the match filter. Digital micro-mirror and/or deformablemicro-mirror eletro-optic mechanisms incorporated into a digitallydriven SLM would also be appropriate for directing light reflected fromits read face 42 for scanning or jittering the focal region of thecoherent fingerprint image beam 44 in the X-Y plane of the match filter.[See, for example U.S. Pat. No. 5,612,713 Bhuva, et al "DigitalMicro-Mirror Device With Block Data Loading"; U.S. Pat. No. 5,471,584,Blaxtan, et. al. "Spatial Light Modulator With Sub-Divided ModulationElements"; U.S. Pat. No. 4,295,710, Heinz, T. "Deformable Mirror WithDither" and U.S. Pat. No. 5,396,364 O'Meara: et al "ContinuouslyOperated Spatial Light Modulator Apparatus And Method".]

Referring to FIG. 4, in the computer addressed verification system, afingerprint image scanner 57 captures and generates an undistorted videoimage fingerprint which is digitized or otherwise operated on usingconventional techniques for allowing a computer system 58 driving theSLM to place a graphical representation of the captured fingerprintimage onto the write face 41 of the SLM. As with the previouslydescribed larger optical table set-up (FIG. 2) the fingerprint imagepresented to the computer system 58 could electronically originate fromanother source, such as a database created from flat, ink-basedfingerprint records. This would allow verification or comparison ofstored fingerprint data with that pre-recorded on a matched filterprovided by a presenting individual. As previously pointed out, thecomputer system 58 can be appropriately programmed to jitter thefingerprint image written to the write face 41 and reflected from theread face 42 of the SLM.

The skilled optical designer should appreciate that when scaling downfrom large and stable optical table set-up, besides concern about spacefor component layout, attention must be paid to location of thermalloads and heat sinks, and the affect such thermal factors can have onoptical parameters of the device. In miniaturization, particularly ofverification devices, the objective is to assure a constant optical pathlength for a chosen wavelength of light between the read face 42 of theSLM and the hologram plane where a holographic matched filter must beconsistently and precisely either mechanically mounted or loaded forinterrogation. Details of location of power supplies, and mechanisms fordissipating thermal energy generated by the electrically drivencomponents is a well developed field and technical discipline, andreference should made to those published teachings and suggestions indesigning the verification and recording components of the inventedsystem. As well, the mechanical mechanisms that mount, load and reloadthe matched filters and position them precisely in the hologram plane ofthe device are not described. The skilled optical designer shouldconsult and follow published teachings and suggestions in the mechanicalarts and disciplines in selecting suitable means and mechanisms forprecision placement or positioning of a framed planar body of arelatively flexible (film) material (the pre-recorded hologram matchedfilter) in a particular plane.

It should also be born in mind, that the verification component of theinvented system is the principal field device of the invented system. Itis a device that will be located at numerous different physicallocations in the field and will be used to transform and comparefingerprint images captured from different individuals to pre-recordedtransformed fingerprint images in matched filters. In contrast, therecording component of the invented system can be centralized and largestable optical set-ups maybe practical. The recording component shouldhave sufficient flexibility optically allow a single recording apparatusto be used for recording matched filters for different types orcategories of field verification devices, i.e. sufficient flexibility toallow for correlation of optical path length for recording to that ofthe particular verification apparatus in which the recorded matchedfilter is expected to be mounted or loaded for subsequent interrogationby a real-time captured, and Fourier transformed fingerprint image.

Basically there should be two different categories of verificationapparatus, Private Key Verification Systems [PKVS] and a PublicIdentification Verification Systems [PIVS].

The Private Key Verification Device [PKVS] should have, in essence, asingle, permanently, or infrequently remounted, pre-recorded matchedfilter for verifying the identity of a single or `few` presentingindividuals to allow access to, for example, a computer workstation, acar, a database storage system, or a physical location. In particular,more than one Fourier transformed matched filter image could bepre-recorded in the hologram mounted as the matched filter each with theconstructing reference beam at a slightly different angle such thatmatch signals for a `few` different individuals are optically projectedat different locations in the photo-diode array. In this way, the dataprocessing system receiving and processing the match signals if any fromthe photo-diode array, could be used not only to allow access of two ormore individuals (husband & wife) to a common device such as a car, butalso could set the parameters of access permitted different individualssuch as family members to a computer system.

In contrast, Public Identification Verification Systems [PIVS] includemechanisms for loading and positioning cards or other objects containingoptically accessible, pre-recorded, matched filters supplied by anypresenting individual or third party for verifying that the fingerprint(identity) of the presenting individual is the same as that pre-recordedin the presented matched filter. Public identification systems [PIVS]could also include sub-systems for retrieving `sheltered`privateinformation that may also be recorded and stored in the pre-recordedhologram matched filter per the teachings of Barbanell (supra) U.S. Pat.No. 5,095,194.

Finally, those skilled in optical scanning and image/pattern recognitionand conversion art will recognize that the respective recording andverification components of the invented real time fingerprint sensor andverification system may also have utility for converting existing flat,ink-based fingerprint paper records into optically addressable recordsand even digital signal addressable records, which could be thenwinnowed and interrogated by anomalous fingerprint images subsequentlycaptured and recorded, either as an actual ,or as a Fourier transform ofa flat, dimensionally undistorted image.

The invented real time fingerprint verification system has beendescribed in context of large optical table set-ups which demonstratethe principles and functionality of the invention. It has also beendescribed in context of preliminary `breadboard` miniaturizedembodiments of verification devices. Skilled optical technologist shouldrecognize and appreciate: (i) the described large optical table sets canbe modified and optimized into a component suitable for large(commercial) scale recording of holographic Fourier transformed imagesof undistorted fingerprints, i.e., fingerprint matched filters; and (ii)the `breadboard` miniaturized verification devices can be modified andoptimized into particular commercial verification components forcomparing a fingerprint image of a presenting individual with thatpre-recorded in a mounted or loaded matched filter. Accordingly, whilemodifications of optical and mechanical components improving andoptimizing performance of the invented real time fingerprintverification system may well comprise independent invention which is notdescribed herein, real time fingerprint verification systemincorporating such improved and optimized components will still fallwithin the spirit and the scope of invention as described and set forthin the appended claims.

We claim:
 1. An optical apparatus suited for recording fingerprinthologram matched filters comprising in combination:a. a scanner forgenerating a flat, dimensionally undistorted, high contrast, fingerprintlight image; b. a recording, intensity sensitive, spatial lightmodulator (RSLM) having planar write and read faces receiving the flat,dimensionally undistorted, high contrast fingerprint light image fromthe scanner on its write face, c. a common source of coherent lightproviding a collimated, coherent light, object beam and a collimated,coherent light, reference beam wherein:(i) the object beam is directedto the planar read face of the recording spatial light modulator (RSLM)for transforming the received, flat, high contrast fingerprint imagereceived by the planar `write` face of the spatial light modulator(RSLM) into a planar coherent light fingerprint image; and (ii) thereference beam is directed to a hologram plane located an optical pathlength (MF) from the read face of the spatial light modulator (RSLM)determined for assuring phase correlation with an interrogating,coherent light object beam image of a fingerprint read from a read faceof a verifying spatial light modulator (VSLM) of a verification opticalfingerprint apparatus, d. means for optically directing the planar,coherent light fingerprint image from the spatial light modulator to aFourier transform focus creating a coherent light, phase distributionimage of the fingerprint in a focal plane; e. a lens optically expandingthe coherent light, phase distribution image of the fingerprint in thefocal plane; f. an optical element blocking a central region of theexpanded, coherent light, phase distribution image of the fingerprinteliminating a central region from the phase distribution image; g. meansfor optically directing the expanded and blocked coherent light, phasedistribution image of the fingerprint to the hologram plane; and h. anoptically sensitive material located in the hologram plane for recordinga hologram of the reference beam and the expanded and blocked coherentlight, phase distribution image of the fingerprint, whereby, thehologram once developed is suitable as a match filter for anyverification optical fingerprint apparatus presenting an interrogating,coherent light object beam of a comparison fingerprint, optical pathlength (MF) from a read face of a verifying spatial light modulator(VSLM).
 2. The optical apparatus of claim 1 further including means foradjusting optical path length respectively of the reference beam and theobject beam to the hologram plane, whereby, matched filters may berecorded with optical path lengths correlated for specific opticalsystems contemplated for optically interrogating the particular recordedmatched filters.
 3. The optical apparatus of claim 1 wherein theexpanded and blocked coherent light phase distribution image of thefingerprint is directed to the hologram plane along an optical axiswhich intersects with the reference beam at an angle θ in a horizontalplane perpendicular to the hologram plane, and further including meansfor polarizing the coherent light of the reference beam and the coherentlight of the expanded and blocked phase distribution image of thefingerprint vertically with respect to such horizontal plane.
 4. Theoptical apparatus of claim 1 wherein the means for generating a flat,dimensionally undistorted, high contrast, fingerprint image comprises incombination(i) a prism having a base surface, at least one slanted sideinput surface and a top transmission surface parallel its base surface,(ii)) a flat holographic phase grating having an one flat surfaceoptically coupled with the base surface of the prism and an exteriorsurface; (iii)) a thin transparent coverslip optically coupled with,covering and protecting the exterior surface of the holographic phasegrating presenting a surface upon which a finger may be pressed toprovide a finger-surface interface which both reflects and transmitslight, the holographic phase grating diffracting illuminating lighttotally internally reflecting from the finger-surface interface topropagate as a converging light beam having an axis normally oriented(⊥) with respect to the base and top transmission surfaces of the prism;d) a source of light for illuminating the finger-surface interfacethrough the slanted side input surface of the prism, the illuminatinglight being refracted and absorbed in areas where finger surface ridgesare in contact with the transparent coverslip, and being totallyinternally reflected in areas corresponding to valleys between and poresin the finger surface ridges not in contact with the transparentcoverslip,the total internally reflected light from the finger-surfaceinterface propagating as a converging beam to, through and out the toptransmission surface of the trapezoidal prism, the converging beam oflight containing a true image of the finger-surface interface whereinthe areas corresponding to finger surface ridges in contact with thecoverslip are dark, the areas corresponding to valleys between and poresin the finger surface ridges not in contact with the coverslip arebright.
 5. The optical apparatus of claim 1 wherein the means forgenerating a flat, dimensionally undistorted, high contrast, fingerprintimage comprises in combination,(i) a right angled prism having ahypotenuse surface and a first and a second right angle surface, (ii) aholographic phase grating plate having a plate surface optically coupledwith the first right angle transmission surface of the prism and anexterior plate surface for diffracting light totally internallyreflecting from its exterior plate surface to propagate normally (⊥)back into the prism, wherein a finger is pressed against the exteriorplate surface of the holographic phase grating plate providing afinger-surface interface; (iii) a source of light illuminating thefinger-surface interface through the hypotenuse surface of the prism,the illuminating light being refracted and absorbed in areas wherefinger surface ridges are in contact with the exterior plate surface,and being totally internally reflected back into the prism in areascorresponding to valleys between and pores in the finger surface ridgesnot in contact with exterior plate surface of the holographic phasegrating plate,the totally internally reflected light containing a trueimage of the finger-surface interface being reflected out of the secondright angle transmission surface of the prism by the hypotenuse surfaceof the prism, the true image of the finger-surface interface beingoriented a plane parallel to the second right angle transmission surfacefor capture, the areas corresponding to finger surface ridges beingdark, the areas corresponding to valleys between and pores in the fingersurface ridges being bright.
 6. The optical apparatus of claim 1 whereina two dimensional pattern may be written by digital image format dataonto the planar read face of the recording spatial light modulator(RSLM), the collimated coherent light object beam directed to the readface of the spatial light modulator transforming that two dimensionalpattern into a planar coherent light image of that pattern, and whereinthe flat, dimensionally undistorted, high contrast, fingerprint lightimage is replicated as a two dimensional pattern in digital image formatdata which is input into a digital data processing system coupled to therecording spatial light modulator (RSLM) for writing the two dimensionalpattern from the digital image format data derived from the flat,dimensionally undistorted, high contrast, fingerprint light image, tothe planar write face of the spatial light modulator.
 7. The opticalapparatus of claim 1 wherein means for generating a flat, dimensionallyundistorted, high contrast, fingerprint image comprises, incombination:i. a means for providing a bright field having dark patternpresenting a planar image of a fingerprint; j. a camera for receivingand converting the bright field and dark pattern of the planar image ofthe fingerprint into digital image format data; k. a central processingunit (CPU) coupled for:(i) receiving and processing the digital imageformat data from the camera; and (ii) writing a representation of thebright field and dark pattern based upon the digital image format datato the planar `read` face of the spatial light modulator.
 8. The opticalapparatus of claim 7 wherein the means for providing a bright fieldhaving dark pattern presenting a planar image of a fingerprint comprisesa flat, ink-based, manually recorded, fingerprint image.
 9. The opticalapparatus of claim 7 wherein the means for providing a bright fieldhaving dark pattern presenting a planar image of a fingerprint is aphotographic reproduction of a flat, ink-base fingerprint image,manually recorded on paper.
 10. The optical apparatus of claim 7 andfurther including a digital database information storage system coupledto the central processing unit for storing digital image format data fora plurality of fingerprint images, and for providing the centralprocessing unit with digital image format data for particularfingerprint images upon request.
 11. The optical apparatus of claim 7wherein the representation of the bright field and dark pattern basedupon the digital image format data written by the CPU to the planar readface of the spatial light modulator has a dark field and a brightpattern.
 12. A method for recording fingerprint hologram matched filterscomprising the steps of:a. generating a flat, dimensionally undistorted,high contrast, fingerprint light image; b. optically projecting the flatdimensionally undistorted, high contrast, fingerprint image onto aplanar write face of a recording intensity sensitive spatial lightmodulator (RSLM); c. providing a collimated, coherent light, object beamand a collimated, coherent light, reference beam from a common source ofcoherent light wherein: (i) the object beam is directed for reflectionfrom a planar `read` face of the recording, intensity sensitive spatiallight modulator (RSLM) to create a planar, coherent light fingerprintimage; and (ii) the reference beam is directed to a hologram plane; d.selecting an optical path length (MF) measured from the read face of therecording spatial light modulator (RSLM) to the hologram plane forassuring phase correlation with a interrogating, coherent light objectbeam image of a fingerprint read from a read face of a verifying spatiallight modulator (VSLM) of a chosen verification optical fingerprintapparatus, e. optically directing the planar, coherent light fingerprintimage from the spatial light modulator to a Fourier transform focuscreating a coherent light, phase distribution image of the fingerprintin a focal plane; f. optically expanding the coherent light, phasedistribution image of the fingerprint in the focal plane; g. opticallyblocking a central region of the expanded, coherent light, phasedistribution image of the fingerprint eliminating a central region fromthe phase distribution image; h. optically directing the expanded andblocked coherent light, phase distribution image of the fingerprint tothe hologram plane; and i. recording a hologram of the reference beamand the expanded and blocked, coherent light, phase distribution imageof the fingerprint using an optically sensitive material located in thehologram plane; and j. developing the hologram recorded in the opticallysensitive material creating a match filter suitable for the chosenverification optical fingerprint apparatus.